1. Field of the Invention
The invention relates to a direct light guide structure, a light guide plate and a back-lit module, and more particularly to the direct light guide plate and the back-lit light module that implement a direct light guide structure to achieve advantages in better uniformity of back lights, higher efficiency of luminance, fewer point-light sources required, lower cost, narrower side-frames and less thickness.
2. Description of the Prior Art
Currently, in the marketplace, back-lit modules for optical display devices can be mainly classified into a group of edge back-lit light guide plates and another group of direct back-lit light guide plates. The back-lit module of the edge back-lit light guide plate has a major disadvantage in emission efficiency. The reason for such a shortcoming is that plural light sources (particularly, LEDs, the point light sources) constructed on one lateral side surface of the light guide plate can only provide one half of the emission lights at most to penetrate the light-ejection surface of the light guide plate. However, on the other hand, the back-lit module of the conventional direct back-lit light guide plate can provide better emission efficiency. Actually, in the direct back-lit light guide plate, the light source (also particularly, LEDs, the point light sources) is directly constructed the other side of the surface of the light guide plate facing the light-ejection surface, and thus the light source is physically to emit at the light-ejection surface. Therefore, the back-lit module of the edge back-lit light guide plate presents much more serious problems in phenomena of light spots and dark spots.
Referring now to FIG. 1A and FIG. 1B, a thin direct back-lit module disclosed by Taiwan utility patent No. M462874 includes a plurality of LED light sources 0100 evenly distributed on the opposing side (bottom surface in the figure) of the light guide plate 0212 with respect to the light-ejection surface (top surface in the figure). On the light-ejection surface (top surface) of the light guide plate 0212, a plurality of concave structures 0202 is included, and each f the concave structures 0202 is set to be disposed correspondingly one LED light source 0100 located on the bottom surface. Thereby, the concave structures 0202 can be used to reflect the rays emitted by the corresponding LED light source 0100, such that uniformity of illumination can be obtained. However, in applying M462874, if the concave structures 0202 contribute a perfect total reflection, the visible region would meet a problem of central dark spotting, which requires a wavy surface structure or designed scratches to resort. Contrarily, if the total reflection is poor, then the visible region would meet a problem of light spotting. In this circumstance, the inclined contour of the concave structure 0202 shall be purposely to include two light segments with different slopes, and thus the surface is not smooth, the total reflection would be even poorer, the light loss would be high, and the manufacturing to produce such a contour for the concave structure 0202 would be more difficult. Thus, further improvement thereupon is definite.
In the Japan Patent Publication No. JPA 2008078089, an LED illumination apparatus includes a plurality of LED light source to encircle the lower rim of the light guide plate, and concave structures are located at the upper rim thereof in correspondence with the LED light sources. However, similar technical shortcomings met in JPA 2008078089, as described in M462874, that the contour of the concave structure is not smooth, though continuous, for consisting a number of connected curve segments with at least two different curvatures. Definitely, the segmented contour can't present a satisfied total reflection and venerable to lose lights.
In addition, in Taiwan Patent Publication No. TW 200925518, an illumination apparatus is to mount a plurality of LED light sources to the lower rim of the light guide plate, and to construct corresponding groove structures on the light guide plate. However, in TW 200925518, both lateral side of the groove structure are individually formed as respective straight lines with fixed slopes, and the slope of the groove bottom is zero. Thus, smoothness is not shown in the contour of the groove structure of TW 200925518. Similar to M462874, contour of the groove structure of TW 200925518 is though continuous, but not smooth, and can only contribute poor total reflection and is opt to lose lights.